Pervasive developmental disorders are characterised by the presence of abnormalities in social interaction and communication as well as repetitive patterns of behaviours. Although early symptoms of the disorder often appear during the first two years of life, its diagnosis is often delayed. The purpose of this study is to analyse the delay between age at first symptoms and age at diagnosis as well as the characteristics of the first symptoms for the different subcategories of pervasive developmental disorders. The sample consists of 601 children with a diagnosis of a pervasive developmental disorder. Age at first symptoms, age at diagnosis and the type of the first problems are registered. The results show that children with autism show first symptoms at a mean age of 15 months whereas diagnosis is made at a mean age of 76 months. Children with Asperger's syndrome show first symptoms at a mean age of 26 months, while diagnosis is made at the mean age of 110 months. There is still a large delay between the age at which parents first report first symptoms and age at diagnosis. To improve early detection, systematic screening and training of primary care paediatricians should be implemented. (Contains 4 tables.)